"""
A module for reading dvi files output by TeX. Several limitations make
this not (currently) useful as a general-purpose dvi preprocessor, but
it is currently used by the pdf backend for processing usetex text.

Interface::

  with Dvi(filename, 72) as dvi:
      # iterate over pages:
      for page in dvi:
          w, h, d = page.width, page.height, page.descent
          for x,y,font,glyph,width in page.text:
              fontname = font.texname
              pointsize = font.size
              ...
          for x,y,height,width in page.boxes:
              ...

"""
from __future__ import (absolute_import, division, print_function,
                        unicode_literals)

import six
from six.moves import xrange

from collections import namedtuple
import errno
from functools import partial, wraps
import matplotlib
import matplotlib.cbook as mpl_cbook
from matplotlib.compat import subprocess
from matplotlib import rcParams
import numpy as np
import struct
import sys
import os

if six.PY3:
    def ord(x):
        return x

# Dvi is a bytecode format documented in
# http://mirrors.ctan.org/systems/knuth/dist/texware/dvitype.web
# http://texdoc.net/texmf-dist/doc/generic/knuth/texware/dvitype.pdf
#
# The file consists of a preamble, some number of pages, a postamble,
# and a finale. Different opcodes are allowed in different contexts,
# so the Dvi object has a parser state:
#
#   pre:       expecting the preamble
#   outer:     between pages (followed by a page or the postamble,
#              also e.g. font definitions are allowed)
#   page:      processing a page
#   post_post: state after the postamble (our current implementation
#              just stops reading)
#   finale:    the finale (unimplemented in our current implementation)

_dvistate = mpl_cbook.Bunch(pre=0, outer=1, inpage=2, post_post=3, finale=4)

# The marks on a page consist of text and boxes. A page also has dimensions.
Page = namedtuple('Page', 'text boxes height width descent')
Text = namedtuple('Text', 'x y font glyph width')
Box = namedtuple('Box', 'x y height width')


# Opcode argument parsing
#
# Each of the following functions takes a Dvi object and delta,
# which is the difference between the opcode and the minimum opcode
# with the same meaning. Dvi opcodes often encode the number of
# argument bytes in this delta.

def _arg_raw(dvi, delta):
    """Return *delta* without reading anything more from the dvi file"""
    return delta


def _arg(bytes, signed, dvi, _):
    """Read *bytes* bytes, returning the bytes interpreted as a
    signed integer if *signed* is true, unsigned otherwise."""
    return dvi._arg(bytes, signed)


def _arg_slen(dvi, delta):
    """Signed, length *delta*

    Read *delta* bytes, returning None if *delta* is zero, and
    the bytes interpreted as a signed integer otherwise."""
    if delta == 0:
        return None
    return dvi._arg(delta, True)


def _arg_slen1(dvi, delta):
    """Signed, length *delta*+1

    Read *delta*+1 bytes, returning the bytes interpreted as signed."""
    return dvi._arg(delta+1, True)


def _arg_ulen1(dvi, delta):
    """Unsigned length *delta*+1

    Read *delta*+1 bytes, returning the bytes interpreted as unsigned."""
    return dvi._arg(delta+1, False)


def _arg_olen1(dvi, delta):
    """Optionally signed, length *delta*+1

    Read *delta*+1 bytes, returning the bytes interpreted as
    unsigned integer for 0<=*delta*<3 and signed if *delta*==3."""
    return dvi._arg(delta + 1, delta == 3)


_arg_mapping = dict(raw=_arg_raw,
                    u1=partial(_arg, 1, False),
                    u4=partial(_arg, 4, False),
                    s4=partial(_arg, 4, True),
                    slen=_arg_slen,
                    olen1=_arg_olen1,
                    slen1=_arg_slen1,
                    ulen1=_arg_ulen1)


def _dispatch(table, min, max=None, state=None, args=('raw',)):
    """Decorator for dispatch by opcode. Sets the values in *table*
    from *min* to *max* to this method, adds a check that the Dvi state
    matches *state* if not None, reads arguments from the file according
    to *args*.

    *table*
        the dispatch table to be filled in

    *min*
        minimum opcode for calling this function

    *max*
        maximum opcode for calling this function, None if only *min* is allowed

    *state*
        state of the Dvi object in which these opcodes are allowed

    *args*
        sequence of argument specifications:

        ``'raw'``: opcode minus minimum
        ``'u1'``: read one unsigned byte
        ``'u4'``: read four bytes, treat as an unsigned number
        ``'s4'``: read four bytes, treat as a signed number
        ``'slen'``: read (opcode - minimum) bytes, treat as signed
        ``'slen1'``: read (opcode - minimum + 1) bytes, treat as signed
        ``'ulen1'``: read (opcode - minimum + 1) bytes, treat as unsigned
        ``'olen1'``: read (opcode - minimum + 1) bytes, treat as unsigned
                     if under four bytes, signed if four bytes
    """
    def decorate(method):
        get_args = [_arg_mapping[x] for x in args]

        @wraps(method)
        def wrapper(self, byte):
            if state is not None and self.state != state:
                raise ValueError("state precondition failed")
            return method(self, *[f(self, byte-min) for f in get_args])
        if max is None:
            table[min] = wrapper
        else:
            for i in xrange(min, max+1):
                assert table[i] is None
                table[i] = wrapper
        return wrapper
    return decorate


class Dvi(object):
    """
    A reader for a dvi ("device-independent") file, as produced by TeX.
    The current implementation can only iterate through pages in order,
    and does not even attempt to verify the postamble.

    This class can be used as a context manager to close the underlying
    file upon exit. Pages can be read via iteration. Here is an overly
    simple way to extract text without trying to detect whitespace::

    >>> with matplotlib.dviread.Dvi('input.dvi', 72) as dvi:
    >>>     for page in dvi:
    >>>         print ''.join(unichr(t.glyph) for t in page.text)
    """
    # dispatch table
    _dtable = [None for _ in xrange(256)]
    dispatch = partial(_dispatch, _dtable)

    def __init__(self, filename, dpi):
        """
        Read the data from the file named *filename* and convert
        TeX's internal units to units of *dpi* per inch.
        *dpi* only sets the units and does not limit the resolution.
        Use None to return TeX's internal units.
        """
        matplotlib.verbose.report('Dvi: ' + filename, 'debug')
        self.file = open(filename, 'rb')
        self.dpi = dpi
        self.fonts = {}
        self.state = _dvistate.pre
        self.baseline = self._get_baseline(filename)

    def _get_baseline(self, filename):
        if rcParams['text.latex.preview']:
            base, ext = os.path.splitext(filename)
            baseline_filename = base + ".baseline"
            if os.path.exists(baseline_filename):
                with open(baseline_filename, 'rb') as fd:
                    l = fd.read().split()
                height, depth, width = l
                return float(depth)
        return None

    def __enter__(self):
        return self

    def __exit__(self, etype, evalue, etrace):
        self.close()

    def __iter__(self):
        """
        Iterate through the pages of the file.

        Returns (text, boxes) pairs, where:
          text is a list of (x, y, fontnum, glyphnum, width) tuples
          boxes is a list of (x, y, height, width) tuples

        The coordinates are transformed into a standard Cartesian
        coordinate system at the dpi value given when initializing.
        The coordinates are floating point numbers, but otherwise
        precision is not lost and coordinate values are not clipped to
        integers.
        """
        while True:
            have_page = self._read()
            if have_page:
                yield self._output()
            else:
                break

    def close(self):
        """
        Close the underlying file if it is open.
        """
        if not self.file.closed:
            self.file.close()

    def _output(self):
        """
        Output the text and boxes belonging to the most recent page.
        page = dvi._output()
        """
        minx, miny, maxx, maxy = np.inf, np.inf, -np.inf, -np.inf
        maxy_pure = -np.inf
        for elt in self.text + self.boxes:
            if isinstance(elt, Box):
                x, y, h, w = elt
                e = 0           # zero depth
            else:               # glyph
                x, y, font, g, w = elt
                h, e = font._height_depth_of(g)
            minx = min(minx, x)
            miny = min(miny, y - h)
            maxx = max(maxx, x + w)
            maxy = max(maxy, y + e)
            maxy_pure = max(maxy_pure, y)

        if self.dpi is None:
            # special case for ease of debugging: output raw dvi coordinates
            return Page(text=self.text, boxes=self.boxes,
                        width=maxx-minx, height=maxy_pure-miny,
                        descent=maxy-maxy_pure)

        # convert from TeX's "scaled points" to dpi units
        d = self.dpi / (72.27 * 2**16)
        if self.baseline is None:
            descent = (maxy - maxy_pure) * d
        else:
            descent = self.baseline

        text = [Text((x-minx)*d, (maxy-y)*d - descent, f, g, w*d)
                for (x, y, f, g, w) in self.text]
        boxes = [Box((x-minx)*d, (maxy-y)*d - descent, h*d, w*d)
                 for (x, y, h, w) in self.boxes]

        return Page(text=text, boxes=boxes, width=(maxx-minx)*d,
                    height=(maxy_pure-miny)*d, descent=descent)

    def _read(self):
        """
        Read one page from the file. Return True if successful,
        False if there were no more pages.
        """
        while True:
            byte = ord(self.file.read(1)[0])
            self._dtable[byte](self, byte)
            if byte == 140:                         # end of page
                return True
            if self.state == _dvistate.post_post:   # end of file
                self.close()
                return False

    def _arg(self, nbytes, signed=False):
        """
        Read and return an integer argument *nbytes* long.
        Signedness is determined by the *signed* keyword.
        """
        str = self.file.read(nbytes)
        value = ord(str[0])
        if signed and value >= 0x80:
            value = value - 0x100
        for i in range(1, nbytes):
            value = 0x100*value + ord(str[i])
        return value

    @dispatch(min=0, max=127, state=_dvistate.inpage)
    def _set_char_immediate(self, char):
        self._put_char_real(char)
        self.h += self.fonts[self.f]._width_of(char)

    @dispatch(min=128, max=131, state=_dvistate.inpage, args=('olen1',))
    def _set_char(self, char):
        self._put_char_real(char)
        self.h += self.fonts[self.f]._width_of(char)

    @dispatch(132, state=_dvistate.inpage, args=('s4', 's4'))
    def _set_rule(self, a, b):
        self._put_rule_real(a, b)
        self.h += b

    @dispatch(min=133, max=136, state=_dvistate.inpage, args=('olen1',))
    def _put_char(self, char):
        self._put_char_real(char)

    def _put_char_real(self, char):
        font = self.fonts[self.f]
        if font._vf is None:
            self.text.append(Text(self.h, self.v, font, char,
                                  font._width_of(char)))
        else:
            scale = font._scale
            for x, y, f, g, w in font._vf[char].text:
                newf = DviFont(scale=_mul2012(scale, f._scale),
                               tfm=f._tfm, texname=f.texname, vf=f._vf)
                self.text.append(Text(self.h + _mul2012(x, scale),
                                      self.v + _mul2012(y, scale),
                                      newf, g, newf._width_of(g)))
            self.boxes.extend([Box(self.h + _mul2012(x, scale),
                                   self.v + _mul2012(y, scale),
                                   _mul2012(a, scale), _mul2012(b, scale))
                               for x, y, a, b in font._vf[char].boxes])

    @dispatch(137, state=_dvistate.inpage, args=('s4', 's4'))
    def _put_rule(self, a, b):
        self._put_rule_real(a, b)

    def _put_rule_real(self, a, b):
        if a > 0 and b > 0:
            self.boxes.append(Box(self.h, self.v, a, b))

    @dispatch(138)
    def _nop(self, _):
        pass

    @dispatch(139, state=_dvistate.outer, args=('s4',)*11)
    def _bop(self, c0, c1, c2, c3, c4, c5, c6, c7, c8, c9, p):
        self.state = _dvistate.inpage
        self.h, self.v, self.w, self.x, self.y, self.z = 0, 0, 0, 0, 0, 0
        self.stack = []
        self.text = []          # list of Text objects
        self.boxes = []         # list of Box objects

    @dispatch(140, state=_dvistate.inpage)
    def _eop(self, _):
        self.state = _dvistate.outer
        del self.h, self.v, self.w, self.x, self.y, self.z, self.stack

    @dispatch(141, state=_dvistate.inpage)
    def _push(self, _):
        self.stack.append((self.h, self.v, self.w, self.x, self.y, self.z))

    @dispatch(142, state=_dvistate.inpage)
    def _pop(self, _):
        self.h, self.v, self.w, self.x, self.y, self.z = self.stack.pop()

    @dispatch(min=143, max=146, state=_dvistate.inpage, args=('slen1',))
    def _right(self, b):
        self.h += b

    @dispatch(min=147, max=151, state=_dvistate.inpage, args=('slen',))
    def _right_w(self, new_w):
        if new_w is not None:
            self.w = new_w
        self.h += self.w

    @dispatch(min=152, max=156, state=_dvistate.inpage, args=('slen',))
    def _right_x(self, new_x):
        if new_x is not None:
            self.x = new_x
        self.h += self.x

    @dispatch(min=157, max=160, state=_dvistate.inpage, args=('slen1',))
    def _down(self, a):
        self.v += a

    @dispatch(min=161, max=165, state=_dvistate.inpage, args=('slen',))
    def _down_y(self, new_y):
        if new_y is not None:
            self.y = new_y
        self.v += self.y

    @dispatch(min=166, max=170, state=_dvistate.inpage, args=('slen',))
    def _down_z(self, new_z):
        if new_z is not None:
            self.z = new_z
        self.v += self.z

    @dispatch(min=171, max=234, state=_dvistate.inpage)
    def _fnt_num_immediate(self, k):
        self.f = k

    @dispatch(min=235, max=238, state=_dvistate.inpage, args=('olen1',))
    def _fnt_num(self, new_f):
        self.f = new_f

    @dispatch(min=239, max=242, args=('ulen1',))
    def _xxx(self, datalen):
        special = self.file.read(datalen)
        if six.PY3:
            chr_ = chr
        else:
            def chr_(x):
                return x
        matplotlib.verbose.report(
            'Dvi._xxx: encountered special: %s'
            % ''.join([(32 <= ord(ch) < 127) and chr_(ch)
                       or '<%02x>' % ord(ch)
                       for ch in special]),
            'debug')

    @dispatch(min=243, max=246, args=('olen1', 'u4', 'u4', 'u4', 'u1', 'u1'))
    def _fnt_def(self, k, c, s, d, a, l):
        self._fnt_def_real(k, c, s, d, a, l)

    def _fnt_def_real(self, k, c, s, d, a, l):
        n = self.file.read(a + l)
        fontname = n[-l:].decode('ascii')
        tfm = _tfmfile(fontname)
        if tfm is None:
            if six.PY2:
                error_class = OSError
            else:
                error_class = FileNotFoundError
            raise error_class("missing font metrics file: %s" % fontname)
        if c != 0 and tfm.checksum != 0 and c != tfm.checksum:
            raise ValueError('tfm checksum mismatch: %s' % n)

        vf = _vffile(fontname)

        self.fonts[k] = DviFont(scale=s, tfm=tfm, texname=n, vf=vf)

    @dispatch(247, state=_dvistate.pre, args=('u1', 'u4', 'u4', 'u4', 'u1'))
    def _pre(self, i, num, den, mag, k):
        comment = self.file.read(k)
        if i != 2:
            raise ValueError("Unknown dvi format %d" % i)
        if num != 25400000 or den != 7227 * 2**16:
            raise ValueError("nonstandard units in dvi file")
            # meaning: TeX always uses those exact values, so it
            # should be enough for us to support those
            # (There are 72.27 pt to an inch so 7227 pt =
            # 7227 * 2**16 sp to 100 in. The numerator is multiplied
            # by 10^5 to get units of 10**-7 meters.)
        if mag != 1000:
            raise ValueError("nonstandard magnification in dvi file")
            # meaning: LaTeX seems to frown on setting \mag, so
            # I think we can assume this is constant
        self.state = _dvistate.outer

    @dispatch(248, state=_dvistate.outer)
    def _post(self, _):
        self.state = _dvistate.post_post
        # TODO: actually read the postamble and finale?
        # currently post_post just triggers closing the file

    @dispatch(249)
    def _post_post(self, _):
        raise NotImplementedError

    @dispatch(min=250, max=255)
    def _malformed(self, offset):
        raise ValueError("unknown command: byte %d", 250 + offset)


class DviFont(object):
    """
    Object that holds a font's texname and size, supports comparison,
    and knows the widths of glyphs in the same units as the AFM file.
    There are also internal attributes (for use by dviread.py) that
    are *not* used for comparison.

    The size is in Adobe points (converted from TeX points).

    .. attribute:: texname

       Name of the font as used internally by TeX and friends. This
       is usually very different from any external font names, and
       :class:`dviread.PsfontsMap` can be used to find the external
       name of the font.

    .. attribute:: size

       Size of the font in Adobe points, converted from the slightly
       smaller TeX points.

    .. attribute:: widths

       Widths of glyphs in glyph-space units, typically 1/1000ths of
       the point size.

    """
    __slots__ = ('texname', 'size', 'widths', '_scale', '_vf', '_tfm')

    def __init__(self, scale, tfm, texname, vf):
        if six.PY3 and isinstance(texname, bytes):
            texname = texname.decode('ascii')
        self._scale, self._tfm, self.texname, self._vf = \
            scale, tfm, texname, vf
        self.size = scale * (72.0 / (72.27 * 2**16))
        try:
            nchars = max(tfm.width) + 1
        except ValueError:
            nchars = 0
        self.widths = [(1000*tfm.width.get(char, 0)) >> 20
                       for char in xrange(nchars)]

    def __eq__(self, other):
        return self.__class__ == other.__class__ and \
            self.texname == other.texname and self.size == other.size

    def __ne__(self, other):
        return not self.__eq__(other)

    def _width_of(self, char):
        """
        Width of char in dvi units. For internal use by dviread.py.
        """

        width = self._tfm.width.get(char, None)
        if width is not None:
            return _mul2012(width, self._scale)

        matplotlib.verbose.report(
            'No width for char %d in font %s' % (char, self.texname),
            'debug')
        return 0

    def _height_depth_of(self, char):
        """
        Height and depth of char in dvi units. For internal use by dviread.py.
        """

        result = []
        for metric, name in ((self._tfm.height, "height"),
                             (self._tfm.depth, "depth")):
            value = metric.get(char, None)
            if value is None:
                matplotlib.verbose.report(
                    'No %s for char %d in font %s' % (
                        name, char, self.texname),
                    'debug')
                result.append(0)
            else:
                result.append(_mul2012(value, self._scale))
        return result


# The virtual font format is a derivative of dvi:
# http://mirrors.ctan.org/info/knuth/virtual-fonts
# The following class reuses some of the machinery of Dvi
# but replaces the _read loop and dispatch mechanism.


class Vf(Dvi):
    """
    A virtual font (\*.vf file) containing subroutines for dvi files.

    Usage::

      vf = Vf(filename)
      glyph = vf[code]
      glyph.text, glyph.boxes, glyph.width
    """

    def __init__(self, filename):
        Dvi.__init__(self, filename, 0)
        try:
            self._first_font = None
            self._chars = {}
            self._read()
        finally:
            self.close()

    def __getitem__(self, code):
        return self._chars[code]

    def _read(self):
        """
        Read one page from the file. Return True if successful,
        False if there were no more pages.
        """
        packet_len, packet_char, packet_width = None, None, None
        while True:
            byte = ord(self.file.read(1)[0])
            # If we are in a packet, execute the dvi instructions
            if self.state == _dvistate.inpage:
                byte_at = self.file.tell()-1
                if byte_at == packet_ends:
                    self._finalize_packet(packet_char, packet_width)
                    packet_len, packet_char, packet_width = None, None, None
                    # fall through to out-of-packet code
                elif byte_at > packet_ends:
                    raise ValueError("Packet length mismatch in vf file")
                else:
                    if byte in (139, 140) or byte >= 243:
                        raise ValueError(
                            "Inappropriate opcode %d in vf file" % byte)
                    Dvi._dtable[byte](self, byte)
                    continue

            # We are outside a packet
            if byte < 242:          # a short packet (length given by byte)
                packet_len = byte
                packet_char, packet_width = self._arg(1), self._arg(3)
                packet_ends = self._init_packet(byte)
                self.state = _dvistate.inpage
            elif byte == 242:       # a long packet
                packet_len, packet_char, packet_width = \
                            [self._arg(x) for x in (4, 4, 4)]
                self._init_packet(packet_len)
            elif 243 <= byte <= 246:
                k = self._arg(byte - 242, byte == 246)
                c, s, d, a, l = [self._arg(x) for x in (4, 4, 4, 1, 1)]
                self._fnt_def_real(k, c, s, d, a, l)
                if self._first_font is None:
                    self._first_font = k
            elif byte == 247:       # preamble
                i, k = self._arg(1), self._arg(1)
                x = self.file.read(k)
                cs, ds = self._arg(4), self._arg(4)
                self._pre(i, x, cs, ds)
            elif byte == 248:       # postamble (just some number of 248s)
                break
            else:
                raise ValueError("unknown vf opcode %d" % byte)

    def _init_packet(self, pl):
        if self.state != _dvistate.outer:
            raise ValueError("Misplaced packet in vf file")
        self.h, self.v, self.w, self.x, self.y, self.z = 0, 0, 0, 0, 0, 0
        self.stack, self.text, self.boxes = [], [], []
        self.f = self._first_font
        return self.file.tell() + pl

    def _finalize_packet(self, packet_char, packet_width):
        self._chars[packet_char] = Page(
            text=self.text, boxes=self.boxes, width=packet_width,
            height=None, descent=None)
        self.state = _dvistate.outer

    def _pre(self, i, x, cs, ds):
        if self.state != _dvistate.pre:
            raise ValueError("pre command in middle of vf file")
        if i != 202:
            raise ValueError("Unknown vf format %d" % i)
        if len(x):
            matplotlib.verbose.report('vf file comment: ' + x, 'debug')
        self.state = _dvistate.outer
        # cs = checksum, ds = design size


def _fix2comp(num):
    """
    Convert from two's complement to negative.
    """
    assert 0 <= num < 2**32
    if num & 2**31:
        return num - 2**32
    else:
        return num


def _mul2012(num1, num2):
    """
    Multiply two numbers in 20.12 fixed point format.
    """
    # Separated into a function because >> has surprising precedence
    return (num1*num2) >> 20


class Tfm(object):
    """
    A TeX Font Metric file. This implementation covers only the bare
    minimum needed by the Dvi class.

    .. attribute:: checksum

       Used for verifying against the dvi file.

    .. attribute:: design_size

       Design size of the font (in what units?)

    .. attribute::  width

       Width of each character, needs to be scaled by the factor
       specified in the dvi file. This is a dict because indexing may
       not start from 0.

    .. attribute:: height

       Height of each character.

    .. attribute:: depth

       Depth of each character.
    """
    __slots__ = ('checksum', 'design_size', 'width', 'height', 'depth')

    def __init__(self, filename):
        matplotlib.verbose.report('opening tfm file ' + filename, 'debug')
        with open(filename, 'rb') as file:
            header1 = file.read(24)
            lh, bc, ec, nw, nh, nd = \
                struct.unpack(str('!6H'), header1[2:14])
            matplotlib.verbose.report(
                'lh=%d, bc=%d, ec=%d, nw=%d, nh=%d, nd=%d' % (
                    lh, bc, ec, nw, nh, nd), 'debug')
            header2 = file.read(4*lh)
            self.checksum, self.design_size = \
                struct.unpack(str('!2I'), header2[:8])
            # there is also encoding information etc.
            char_info = file.read(4*(ec-bc+1))
            widths = file.read(4*nw)
            heights = file.read(4*nh)
            depths = file.read(4*nd)

        self.width, self.height, self.depth = {}, {}, {}
        widths, heights, depths = \
            [struct.unpack(str('!%dI') % (len(x)/4), x)
             for x in (widths, heights, depths)]
        for idx, char in enumerate(xrange(bc, ec+1)):
            byte0 = ord(char_info[4*idx])
            byte1 = ord(char_info[4*idx+1])
            self.width[char] = _fix2comp(widths[byte0])
            self.height[char] = _fix2comp(heights[byte1 >> 4])
            self.depth[char] = _fix2comp(depths[byte1 & 0xf])


PsFont = namedtuple('Font', 'texname psname effects encoding filename')


class PsfontsMap(object):
    """
    A psfonts.map formatted file, mapping TeX fonts to PS fonts.
    Usage::

     >>> map = PsfontsMap(find_tex_file('pdftex.map'))
     >>> entry = map['ptmbo8r']
     >>> entry.texname
     'ptmbo8r'
     >>> entry.psname
     'Times-Bold'
     >>> entry.encoding
     '/usr/local/texlive/2008/texmf-dist/fonts/enc/dvips/base/8r.enc'
     >>> entry.effects
     {'slant': 0.16700000000000001}
     >>> entry.filename

    For historical reasons, TeX knows many Type-1 fonts by different
    names than the outside world. (For one thing, the names have to
    fit in eight characters.) Also, TeX's native fonts are not Type-1
    but Metafont, which is nontrivial to convert to PostScript except
    as a bitmap. While high-quality conversions to Type-1 format exist
    and are shipped with modern TeX distributions, we need to know
    which Type-1 fonts are the counterparts of which native fonts. For
    these reasons a mapping is needed from internal font names to font
    file names.

    A texmf tree typically includes mapping files called e.g.
    psfonts.map, pdftex.map, dvipdfm.map. psfonts.map is used by
    dvips, pdftex.map by pdfTeX, and dvipdfm.map by dvipdfm.
    psfonts.map might avoid embedding the 35 PostScript fonts (i.e.,
    have no filename for them, as in the Times-Bold example above),
    while the pdf-related files perhaps only avoid the "Base 14" pdf
    fonts. But the user may have configured these files differently.
    """
    __slots__ = ('_font',)

    def __init__(self, filename):
        self._font = {}
        with open(filename, 'rt') as file:
            self._parse(file)

    def __getitem__(self, texname):
        try:
            result = self._font[texname]
        except KeyError:
            result = self._font[texname.decode('ascii')]
        fn, enc = result.filename, result.encoding
        if fn is not None and not fn.startswith('/'):
            fn = find_tex_file(fn)
        if enc is not None and not enc.startswith('/'):
            enc = find_tex_file(result.encoding)
        return result._replace(filename=fn, encoding=enc)

    def _parse(self, file):
        """Parse each line into words."""
        for line in file:
            line = line.strip()
            if line == '' or line.startswith('%'):
                continue
            words, pos = [], 0
            while pos < len(line):
                if line[pos] == '"':   # double quoted word
                    pos += 1
                    end = line.index('"', pos)
                    words.append(line[pos:end])
                    pos = end + 1
                else:                  # ordinary word
                    end = line.find(' ', pos+1)
                    if end == -1:
                        end = len(line)
                    words.append(line[pos:end])
                    pos = end
                while pos < len(line) and line[pos] == ' ':
                    pos += 1
            self._register(words)

    def _register(self, words):
        """Register a font described by "words".

        The format is, AFAIK: texname fontname [effects and filenames]
        Effects are PostScript snippets like ".177 SlantFont",
        filenames begin with one or two less-than signs. A filename
        ending in enc is an encoding file, other filenames are font
        files. This can be overridden with a left bracket: <[foobar
        indicates an encoding file named foobar.

        There is some difference between <foo.pfb and <<bar.pfb in
        subsetting, but I have no example of << in my TeX installation.
        """

        # If the map file specifies multiple encodings for a font, we
        # follow pdfTeX in choosing the last one specified. Such
        # entries are probably mistakes but they have occurred.
        # http://tex.stackexchange.com/questions/10826/
        # http://article.gmane.org/gmane.comp.tex.pdftex/4914

        texname, psname = words[:2]
        effects, encoding, filename = '', None, None
        for word in words[2:]:
            if not word.startswith('<'):
                effects = word
            else:
                word = word.lstrip('<')
                if word.startswith('[') or word.endswith('.enc'):
                    if encoding is not None:
                        matplotlib.verbose.report(
                            'Multiple encodings for %s = %s'
                            % (texname, psname), 'debug')
                    if word.startswith('['):
                        encoding = word[1:]
                    else:
                        encoding = word
                else:
                    assert filename is None
                    filename = word

        eff = effects.split()
        effects = {}
        try:
            effects['slant'] = float(eff[eff.index('SlantFont')-1])
        except ValueError:
            pass
        try:
            effects['extend'] = float(eff[eff.index('ExtendFont')-1])
        except ValueError:
            pass

        self._font[texname] = PsFont(
            texname=texname, psname=psname, effects=effects,
            encoding=encoding, filename=filename)


class Encoding(object):
    """
    Parses a \*.enc file referenced from a psfonts.map style file.
    The format this class understands is a very limited subset of
    PostScript.

    Usage (subject to change)::

      for name in Encoding(filename):
          whatever(name)
    """
    __slots__ = ('encoding',)

    def __init__(self, filename):
        with open(filename, 'rt') as file:
            matplotlib.verbose.report('Parsing TeX encoding ' + filename,
                                      'debug-annoying')
            self.encoding = self._parse(file)
            matplotlib.verbose.report('Result: ' + repr(self.encoding),
                                      'debug-annoying')

    def __iter__(self):
        for name in self.encoding:
            yield name

    def _parse(self, file):
        result = []

        state = 0
        for line in file:
            comment_start = line.find('%')
            if comment_start > -1:
                line = line[:comment_start]
            line = line.strip()

            if state == 0:
                # Expecting something like /FooEncoding [
                if '[' in line:
                    state = 1
                    line = line[line.index('[')+1:].strip()

            if state == 1:
                if ']' in line:  # ] def
                    line = line[:line.index(']')]
                    state = 2
                words = line.split()
                for w in words:
                    if w.startswith('/'):
                        # Allow for /abc/def/ghi
                        subwords = w.split('/')
                        result.extend(subwords[1:])
                    else:
                        raise ValueError("Broken name in encoding file: " + w)

        return result


def find_tex_file(filename, format=None):
    """
    Call :program:`kpsewhich` to find a file in the texmf tree. If
    *format* is not None, it is used as the value for the
    `--format` option.

    Apparently most existing TeX distributions on Unix-like systems
    use kpathsea. It's also available as part of MikTeX, a popular
    distribution on Windows.

    .. seealso::

      `Kpathsea documentation <http://www.tug.org/kpathsea/>`_
        The library that :program:`kpsewhich` is part of.
    """

    cmd = ['kpsewhich']
    if format is not None:
        cmd += ['--format=' + format]
    cmd += [filename]

    matplotlib.verbose.report('find_tex_file(%s): %s'
                              % (filename, cmd), 'debug')
    # stderr is unused, but reading it avoids a subprocess optimization
    # that breaks EINTR handling in some Python versions:
    # http://bugs.python.org/issue12493
    # https://github.com/matplotlib/matplotlib/issues/633
    pipe = subprocess.Popen(cmd, stdout=subprocess.PIPE,
                            stderr=subprocess.PIPE)
    result = pipe.communicate()[0].rstrip()
    matplotlib.verbose.report('find_tex_file result: %s' % result,
                              'debug')
    return result.decode('ascii')

# With multiple text objects per figure (e.g., tick labels) we may end
# up reading the same tfm and vf files many times, so we implement a
# simple cache. TODO: is this worth making persistent?

_tfmcache = {}
_vfcache = {}


def _fontfile(texname, class_, suffix, cache):
    try:
        return cache[texname]
    except KeyError:
        pass

    filename = find_tex_file(texname + suffix)
    if filename:
        result = class_(filename)
    else:
        result = None

    cache[texname] = result
    return result


def _tfmfile(texname):
    return _fontfile(texname, Tfm, '.tfm', _tfmcache)


def _vffile(texname):
    return _fontfile(texname, Vf, '.vf', _vfcache)


if __name__ == '__main__':
    import sys
    matplotlib.verbose.set_level('debug-annoying')
    fname = sys.argv[1]
    try:
        dpi = float(sys.argv[2])
    except IndexError:
        dpi = None
    with Dvi(fname, dpi) as dvi:
        fontmap = PsfontsMap(find_tex_file('pdftex.map'))
        for page in dvi:
            print('=== new page ===')
            fPrev = None
            for x, y, f, c, w in page.text:
                if f != fPrev:
                    print('font', f.texname, 'scaled', f._scale/pow(2.0, 20))
                    fPrev = f
                print(x, y, c, 32 <= c < 128 and chr(c) or '.', w)
            for x, y, w, h in page.boxes:
                print(x, y, 'BOX', w, h)
